Natural Availability of 
Oak Wilt Inocula 
by Endoconidiophora fagacearum Bretz, 
has become increasingly important as a 
destroyer of oak trees in the eastern half 
of the United States. It was first described 
about 13 years ago as a fungus disease in 
Wisconsin (Anonymous 1942), but ear- 
lier reports of dying oaks indicate that it 
probably has been present there for the 
past 20 years. 
The American oaks, which number 
about 300 species, are the most important 
group of hardwoods in North America, 
furnishing more native timber than any 
other related group of broadleaved trees 
(Finlay 1950). In 1948 the net volume of 
saw timber in Illinois totaled 10.3 billion 
board feet (King & Winters 1952). The 
oak species total was 56 per cent of the net 
board-foot volume. White oak accounted 
for 21 per cent of the total, and black oak 
and northern red oak each made up about 
10 per cent. The esthetic as well as the 
commercial value of oaks must be consid- 
ered in evaluating the economic import- 
ance of oak wilt. Oaks are prized highly as 
both shade and ornamental trees. 
No species of oak yet tested has shown 
immunity to oak wilt (Kuntz & Riker 
19505). Other susceptible species of the 
family Fagaceae are Castanea mollissima 
Bl., Chinese chestnut; C. dentata Borkh.., 
American chestnut; C. sativa Mill., Euro- 
pean chestnut; Lithocarpus densiflorus 
Rehd., tanbark oak; and Castanopsis sem- 
pervirens Dudley, bush chinquapin (Bretz 
& Long 1950, Bretz 1952a, Ernst & Bretz 
I: the past 10 years, oak wilt, caused 
* Dr. E. A. Curl, now Assistant Plant Pathologist, 
Alabama Polytechnic Institute, Auburn, Alabama, was a 
Special Research Assistant with the Illinois Natural His- 
tory Survey at the time he made the study reported 
here. The study was made possible through assistance 
provided by the Forest Preserve District of Cook County, 
River Forest, Illinois. This article is based upon a thesis 
submitted by the writer to the Graduate College, Univer- 
sity of Illinois, Urbana, in partial fulfillment of the re- 
quirements for the degree of Doctor of Philosophy in Plant 
Pathology. 
| eA wer On BAMA) Oy 
1953). Once infected, trees in the red oak 
group die rapidly, most of them within 6 
weeks. Trees in the white oak group may 
die slowly over a period of 1 to 3 years. 
Since 1942 oak wilt has been reported 
from 18 states. The results of aerial sur- 
veys (Fowler 1951, 1952, 1953) con- 
ducted by the United States Department 
of Agriculture, Division of Forest Pathol- 
ogy, since 1951 and various individual re- 
ports (Bretz 1949, Carter 1950b, 1952, 
Cummins 1949, Elmer et al. 1953, Fergus 
& Morris 1950, French & Christensen 
1950, Strong 1951, Wysong 1949, Young 
& Bart 1951) indicate a considerable in- 
crease in wilt in most of these states. 
In Illinois the disease was first noticed 
in 1942 (Carter 1950a). By the end of 
1952 it had been found in 54 of the 102 
counties in the state. Most of the coun- 
ties that are still free of the disease are 
located in areas where oak timber is not 
abundant. 
The threat of oak wilt was recognized 
early in Wisconsin (Anonymous 1942, 
Henry et al. 1944) and in Iowa (Dietz & 
Barrett 1946, Dietz & Young 1948), 
where some of the first research on the 
disease was conducted between 1942 and 
1948. In 1950 the National Oak Wilt 
Research Committee (Anonymous 1950) 
was organized at Memphis, Tennessee, for 
the purpose of supporting research pro- 
grams in co-ordination with several uni- 
versities and with the United States De- 
partment of Agriculture, Division of For- 
est Pathology. Such programs have now 
been developed in most of the states in 
which oak wilt is found. 
The studies reported herein are _in- 
tended mainly to supply information con- 
cerning the availability of oak wilt inocula 
and the relative importance of I]linois en- 
vironmental conditions at different times 
of the year on the longevity of the causal 
[277] 
